A thermal dispersion switch/transmitter for determining flow rate and liquid level in a non-contacting apparatus. A special preparation of one or more small spots in the outside surface of the wall of the conduit, standpipe or container enables one or more thermally sensitive elements to reside very close to the fluid on the opposite side of the wall. A temperature sensor is formed of a raster pattern electrical conductor deposited on a thin, electrically insulative, thermally conductive flat chip. One temperature sensor is time-shared and is periodically self heated and functions as the reference as well as the active or heated sensor of the invention. One alternative is to employ two temperature sensors, one being a reference sensor and the other being the active sensor. An alternative embodiment employs the same construction of one or more small, very thin membrane surfaces to which multiple detectors are mounted inside a probe inserted into the conduit. A second alternative embodiment employs the same construction of a very thin, small area spot on the outside of a probe inserted into a conduit or vessel for flow rate, liquid level, or interface sensing. Other embodiments are shown and described. All of the embodiments employ a miniature temperature sensor with the sensing element being self heated, the switch/transmitter being configured to operate at intrinsically safe, 24 VDC, 4-20 mA input power.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A thermal dispersion flow sensing apparatus comprising: a fluid flow conduit having a wall defining the fluid flow path and having at least one detent in said wall adapted to receive a detector element; a detector comprising a temperature sensitive element on an electrically insulative, thermally conductive substrate, said detector being mounted in said detent of said conduit so as to be in thermal communication with the fluid in the conduit; and electrical conductors connected to said temperature sensitive element and adapted to be connected to external signal processing circuitry.
2. The apparatus recited in claim 1 , and further comprising a thermally conductive element between said detector and the fluid in the conduit.
3. The apparatus recited in claim 1 , wherein said detent of said conduit is shaped and configured to reduce lateral heat dissipation and confine heat transfer from said detector to the fluid in the conduit.
4. The apparatus recited in claim 3 , wherein said detent is formed with a generally centrally located pedestal on which said detector is mounted.
5. A thermal dispersion apparatus adapted to sense fluid flow past a surface on one side of a wall, the apparatus comprising: at least one reduced thickness area in said wall; a first detector comprising a first temperature sensitive element for sensing the temperature of a thermally conductive region, said detector being thermally coupled to said reduced thickness area of said wall, said thermally conductive region in said reduced thickness area being shaped and configured to provide an operationally effective thermal transfer between the fluid in contact with said surface and said detector; and means for coupling an operationally effectively power source to said thermally conductive region to effect a temperature differential between said fluid and said thermally conductive region; wherein said first temperature sensitive element is heated by electrical power of such low intensity as to be intrinsically safe.
6. A thermal dispersion switch/transmitter apparatus for selectively sensing flow, mixing, phase, condition, liquid level, and interface between non-miscible materials in a fluid media, said apparatus comprising; a container having a wall for containing the media and having at least one area of reduced thickness in said wall; a first detector comprising a first temperature sensitive element for sensing the temperature of a thermally conductive region, said detector being thermally coupled to said reduced thickness area, said thermally conductive region in said reduced thickness area being shaped and configured to provide an operationally effective thermal transfer between the media in said container and said detector; and an electrical circuit to which said electrical thermally conductive region is coupled, said circuit providing operationally effective power to effect a temperature differential between said thermally conductive region and said media, said circuit having an indicator providing information as to the state of the media in said container in relation to the temperature of said first temperature sensitive element; wherein the electrical power applied to heat said first temperature sensitive element is no more than about 24 VDC with 4-20 mA of current.
7. The apparatus recited in claim 6 , wherein the input 24 VDC power is connected by means of a DC/DC converter from relatively high voltage and low current to a lower voltage and higher current to power the temperature sensitive element.
8. A method of constructing a thermal dispersion switch/transmitter, the method comprising: forming at least one area of reduced thickness in the wall of a fluid conduit; selecting a detector comprising a temperature sensitive element on a thermally conductive substrate; mounting the detector on the reduced thickness area of the fluid conduit wall so that said substrate conforms to the contours of said reduced thickness area; and heating said temperature sensitive element by electrical power of such low intensity as to be intrinsically safe.
9. A method of constructing a thermal dispersion switch/transmitter, the method comprising: forming at least one area of reduced thickness in the wall of a fluid conduit; selecting a solid state detector comprising a temperature sensitive element on a thermally conductive base; mounting the detector on the reduced thickness area of the fluid conduit wall; connecting the detector in an electrical circuit which provides operationally effective power to the detector chip and provides a signal indicative of the fluid flow in the conduit; and heating said temperature sensitive element by electrical power of such low intensity as to be intrinsically safe.
10. A thermal dispersion switch/transmitter comprising: a hollow probe comprising a thermal well, said probe having a proximal end and a distal end separated by an enclosing side wall, said proximal end being shaped and configured to be mounted in the wall of a fluid container; a mounting element secured to and closing said distal end of said probe; a first area of reduced thickness arranged generally normal to the longitudinal axis of and inside said probe; a first detector comprising a first temperature sensitive element on an electrically insulative thermally conductive base, said first detector being mounted in said reduced thickness area within said probe and adapted to be positioned within the fluid in the container, said reduced thickness area being shaped and configured to provide and operationally effective thermal transfer between the fluid in said container and said detector; and means for coupling an operationally effective electrical power source to said first detector to effect a temperature differential between the fluid in the container and said first temperature sensitive element, the electrical power being applied by the power source is of such low intensity as to be intrinsically safe; said one end of said probe being shaped and configured to extend into a fluid flow conduit so that said surface directly contacts the fluid therein and locally generates a flow condition at said temperature sensitive element.
11. A thermal dispersion apparatus adapted to sense fluid flow past a surface on one side of a wall, the apparatus comprising: at least one reduced thickness area in said wall, a first detector comprising a first temperature sensitive element on an electrically insulative, thermally conductive base, said detector being thermally coupled to said reduced thickness area of said wall, said reduced thickness area being shaped and configured to provide an operationally effective thermal transfer between the fluid in contact with said surface and said detector; means for sensing the temperature of said first temperature sensitive element; means for heating said first temperature sensitive element; means for providing input power and control signals to said heating means by electrical power of such low intensity as to be intrinsically safe; and means for transmitting output signals from said temperature sensing means.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
March 14, 2002
September 30, 2003
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